Ultra-long focal length, high-resolution continuous zoom mid-wave infrared optical system

Abstract

The present invention discloses an ultra-long focal length and high-resolution mid-wave infrared continuous zoom optical system, which sequentially includes from the object side: a positive focal power front fixed lens group (G1) that is fixed during zooming, a negative focal power zoom lens group (G2) that moves from the image side to the object side during zooming, a positive focal power compensation lens group (G3) that moves from the object side to the image side during zooming, a negative focal power rear fixed lens group (G4) that is fixed during zooming, and a positive focal power secondary imaging lens group (G5) that is fixed during zooming. The system is adapted to a 1024×768 10-micron cooled mid-wave infrared detector, with a relative aperture of 1:4 and continuous zooming of the focal length from 110 mm to 1500 mm. The present invention solves the problems of inherent secondary spectrum, high-order spherical aberration, chromatic aberration, etc. that are difficult to correct in an ultra-long focal length and large aperture system, and significantly improves the resolution of the optical system. The mechanical compensation two-component zoom form has a simple structure, ensuring the simplicity and stability of the entire optical system.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and particularly relates to the design of a mid-wave and long-wave infrared optical system with an ultra-long focal length, high resolution, and continuous zoom. Background Art

[0002] Infrared thermal imaging technology is a passive infrared night vision technology that uses the difference in the infrared radiation intensity of natural objects to form images, and discovers and identifies targets based on the temperature difference (thermal radiation difference) between the target and the background or between different parts of the target. Infrared thermal imaging technology has the advantages of being unrestricted by day and night, being able to work all day and all weather, having strong smoke penetration ability, anti-electromagnetic interference, good anti-camouflage and detection concealment, and has gradually become a cutting-edge hot topic that scientists from various countries compete to research. In recent years, with the increasing demand for long-distance observation and aiming infrared devices such as border and coastal defense, research on ultra-long focal length continuous zoom infrared imaging systems has been successively carried out at home and abroad, and various forms of infrared zoom designs have emerged in an endless stream. The greatest advantage of an ultra-long focal length continuous zoom system is that it can continuously track the same target while changing the field of view, without causing the loss of the target. It can search the target area with a large field of view and observe the details of long-distance targets with a small field of view.

[0003] In the prior art, the Chinese patent application "30x Mid-wave Infrared Zoom Optical System with Ultra-long Focal Length" (patent publication number CN207636838U) proposed a continuous zoom with a focal length of 40mm to 1200mm, which is adapted to a 640×512 15-micron F4 cooled mid-wave infrared detector; the Chinese patent application "Continuous Zoom Mid-wave Infrared Optical System with Ultra-long Focal Length" (patent publication number CN103823294B) proposed a mid-wave infrared optical system with an aperture of F4, a working band of 3μm to 5μm, and a continuous zoom with a focal length of 88mm to 1100mm, which is adapted to a 640×512 15-micron cooled mid-wave infrared detector. In order to improve the ability of infrared devices to discover and identify targets, it is often desired that the optical system has a longer focal length and higher resolution. The increase in focal length is accompanied by a sharp increase in the aperture of the optical system. In addition to the inherent secondary spectral chromatic aberration, a large amount of higher-order spherical aberration, chromatic aberration, etc. are introduced, making it difficult to correct the aberrations of the optical system; the requirement for high resolution requires good aberration balance correction of the optical system. The requirements of ultra-long focal length zoom and high-resolution imaging restrict each other. In the existing publicly available technologies, the focal length is mostly below 1200mm, and the detector resolution is concentrated at 640×512 15μm, which has not fully met the requirements of ultra-long focal length continuous zoom high-resolution detection. In this context, there is an urgent need to develop an ultra-long focal length, high-resolution, continuous zoom optical system. Summary of the Invention

[0004] The object of the present invention is to overcome the shortcomings of the prior art and propose a high-resolution continuous zoom mid-wave infrared optical system with an ultra-long focal length.

[0005] To achieve the above object, the present invention provides an ultra-long focal length, high-resolution continuous zoom mid-wave infrared optical system, which sequentially includes, from the object side to the image side:

[0006] A front fixed lens group with a positive optical power that is fixed during zooming;

[0007] A zoom lens group that moves from the object side to the image side when zooming from the wide-angle end to the telephoto end;

[0008] A compensation lens group that moves from the image side to the object side when zooming from the wide-angle end to the telephoto end; and

[0009] A rear fixed lens group with a negative optical power that is fixed during zooming, used for focusing and compensating for the thermal defocus of the optical system in high and low temperature working environments;

[0010] A secondary imaging lens group with a positive optical power that is fixed during zooming, used to achieve the front placement of the cold stop of the infrared cooled detector;

[0011] Wherein, when zooming from the wide-angle end to the telephoto end, the zoom lens group and the compensation lens group move towards each other, and the interval between the two components satisfies the following condition:

[0012] (d 23max -d 23min ) / f w >1

[0013] Wherein:

[0014] f w Is the focal length of the optical system at the wide-angle end;

[0015] d 23max Is the maximum value of the interval between the zoom lens group and the compensation lens group during zooming;

[0016] d 23min Is the minimum value of the interval between the zoom lens group and the compensation lens group during zooming.

[0017] According to the above technical solution, the working wavelength band of the optical system is 3.7 - 4.8 μm, and the F# is 4.

[0018] According to the above technical solution, the optical system is adapted to a mid-wave infrared detector with an F-number of 4, a pixel number of 1024×768, and a pixel size of 10 μm or more.

[0019] According to the above technical solution, the front fixed lens group with a positive optical power that is fixed during zooming includes a lens with a positive optical power and a lens with a negative optical power. Both lenses have at least one surface that is meniscus-shaped and curved towards the detector target surface.

[0020] According to the above technical solution, the other surface of the lens with a positive optical power is an aspherical surface.

[0021] Continuing with the above technical solution, the lenses in the zoom lens group and the compensating lens group are all aspherical lenses, and at least one surface is an aspherical diffractive surface.

[0022] Continuing with the above technical solution, the fixed negative focal length rear fixed lens group during zooming includes a meniscus lens with the bending direction towards the object side, and its first surface is aspherical.

[0023] Continuing with the above technical solution, the positive focal length secondary imaging lens group sequentially includes a positive focal length double convex lens, a negative focal length meniscus lens, and a positive focal length meniscus lens from the object side to the image side direction, and at least one surface of at least one lens is aspherical.

[0024] The focal length of the optical system of the present invention is continuously variable. The short focal end is used to search and discover targets, the long focal end is used to track and identify targets, and the target is not lost during the short-long focal length switching. The characteristics of ultra-long focal length imaging and high-resolution imaging at the long focal end of the optical system greatly improve the operating distance of the optical system and enhance the ability to observe target details at long distances.

[0025] Furthermore, aspherical designs are adopted in the lens groups G1, G2, G3, G4, and G5 in the entire infrared optical system to balance the high-order aberrations of the optical system. Among them, the zoom lens group G2 is a diffractive surface lens with an aspherical substrate, which is used to correct the chromatic aberration and secondary spectrum of the optical system. The focal power distribution of the lens groups G1, G2, G3, G4, and G5 is a positive-negative-positive-negative-positive structure. In addition to the conventional combination of silicon and germanium materials, zinc selenide material is used for the lens L53 in the lens group G5 to further balance the residual chromatic aberration of the optical system. The imaging quality is good throughout the entire zoom range, and the image is clear and sharp. Among them, the focal length at the long focal end reaches 1500 mm, and the spot size of the optical system is less than 1 pixel (10 μm), with good imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the ultra-long focal length high-resolution continuous zoom mid-wave infrared optical system according to an embodiment of the present invention;

[0027] Figure 2 It is a schematic diagram of the short-long focal length adjustment of the optical system according to an embodiment of the present invention;

[0028] Figure 3 It is the transfer function curve at the short focal end according to an embodiment of the present invention;

[0029] Figure 4 It is the transfer function curve at the middle focal end according to an embodiment of the present invention;

[0030] Figure 5 It is the transfer function curve at the long focal end according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is a schematic diagram of the optical path of the present invention, corresponding to the lens configuration of Embodiment 1 of the optical system described later. Figures 2 to 4 Corresponding to the transfer function curves of the telephoto end, mid-telephoto end, and wide-angle end of the present invention.

[0032] Figure 1 In the schematic diagram of the optical path of the ultra-long focal length, high-resolution continuous zoom mid-wave infrared optical system shown, the left side is the object side and the right side is the image side along the direction of the light rays. This optical system sequentially includes a front fixed lens group G1 with a positive optical power that is fixed during zooming, a negative optical power zoom lens group G2 that moves from the image side to the object side during zooming, a positive optical power zoom lens group G3 that moves from the object side to the image side during zooming, a rear fixed lens group G4 with a negative optical power that is fixed during zooming, and a positive optical power secondary imaging lens group G5 that is fixed during zooming from the object side to the image side.

[0033] The front fixed lens group G1 with a positive optical power that is fixed during zooming is composed of a lens L11 with a positive optical power and a lens L12 with a negative optical power. Both the lens L11 and the lens L12 are meniscus-shaped, and the lenses are curved towards the detector target surface.

[0034] The front fixed lens group G1 is in a telephoto structure form, elongating the back intercept of the front fixed group, quickly compressing the beam aperture, and reducing the aperture of the subsequent lens groups.

[0035] As Figure 2 shown, when zooming from the wide-angle end to the telephoto end, the zoom lens group G2 and the compensation lens group G3 move towards each other, and the interval between the two components satisfies the following condition: (d 23max -d 23min ) / f w > 1, where f w is the focal length of the wide-angle end optical system; d 23max is the maximum value of the interval between the zoom lens group (G2) and the compensation lens group (G3) during zooming; d 23min is the minimum value of the interval between the zoom lens group (G2) and the compensation lens group (G3) during zooming. Satisfying this condition can suppress the incident angle of the telephoto end beam on the compensation lens group (G3), reduce the optical power of the compensation lens group (G3), and achieve a looser tolerance for the zoom lens.

[0036] The rear fixed lens group (G4) has a focusing function to compensate for the thermal defocus of the optical system in high and low temperature working environments.

[0037] The imaging light rays converge after being refracted by the lens groups G1, G2, G3, and G4, and a primary image point is formed at the air interval between the lens groups G4 and G5. The secondary imaging lens group G5 images the primary image point onto the detector target surface, constituting a secondary imaging optical path structure.

[0038] The secondary imaging lens group (G5) is composed of a positive optical power biconvex lens (L51), a negative optical power meniscus lens (L52) and a positive optical power meniscus lens (L53) in order from the object side. One surface of at least one lens in the secondary imaging lens group (G5) is an aspherical surface. The secondary imaging lens group is used to realize the cold stop front of the infrared cooling detector and 100% cold stop efficiency matching.

[0039] The above optical system is adapted to a 1024×768 10-micron cooled mid- and far-infrared detector with a relative aperture of 1:4 and a focal length of 110mm to 1500mm with continuous zoom.

[0040] The specific design parameters of the optical system embodiment 1 are shown in Table 1.

[0041] Table 1 Optical system design parameter table of specific embodiment 1

[0042]

[0043] In Table 1, the radius of curvature refers to the radius of curvature of each lens surface, the thickness or interval refers to the thickness of the lens or the distance between adjacent lens surfaces, the material refers to the material used for the lens, and the air refers to the medium between the two lenses being air.

[0044] In order to obtain better imaging quality, the optical system adopts aspherical design. The lens surfaces marked with "*" in the table are aspherical.

[0045] The lens groups G1, G2, G3, G4 and G5 in the entire infrared optical system can all use aspheric designs to balance the high-level aberrations of the optical system. Among them, the zoom lens group G2 is a diffractive lens with an aspheric substrate, which is used to correct the chromatic aberration and secondary spectrum of the optical system. The focal length of the lens groups G1, G2, G3, G4 and G5 is distributed as a positive-negative-positive-negative-positive structure. In addition to the conventional silicon and germanium material combination, the lens L53 in the lens group G5 uses zinc selenide material to further balance the residual chromatic aberration of the optical system. The optical imaging quality is good throughout the zoom range, and the image is clear and sharp. Among them, the focal length of the telephoto end is 1500mm, and the optical system dispersion spot is less than 1 pixel (10μm), with good imaging quality.

[0046] Figures 3 to 5 This is a simulation data diagram of the optical transfer function of the optical system of the present invention. Among them: Figure 3 This is a transfer function curve of the patented optical system when the short focal end is 50lp / mm; Figure 4 This is a transfer function curve of the optical system of the patent when the focal end is 50lp / mm; Figure 5 This is a transfer function curve of the patented optical system at the telephoto end at 50lp / mm.

[0047] In summary, through reasonable optical path layout and ingenious material combination, and by introducing aspherical and diffractive surfaces on the aberration-sensitive surface to correct aberrations, the optical system of the present invention solves the problems of inherent secondary spectrum, high-order spherical aberration, chromatic aberration, etc. that are difficult to correct in ultra-long focal length and large aperture systems, and significantly improves the resolution of the optical system. The mechanical compensation two-component zoom form has a simple structure, ensuring the simplicity and stability of the entire optical system.

[0048] Finally, it should be noted that the present invention is not limited to the above embodiments. Those skilled in the art should understand that modifications or equivalent replacements can be made without departing from the spirit of the present invention.

Claims

1. An ultra-long focal length, high-resolution continuous zoom mid-wave infrared optical system, characterized in that, The optical system successively includes, from the object side to the image side: A front fixed lens group (G1) with a positive optical power that is fixed during zooming, which is used to elongate the back intercept of the front fixed group; A zoom lens group (G2), which moves from the object side to the image side when zooming from the wide-angle end to the telephoto end; A compensation lens group (G3), which moves from the image side to the object side when zooming from the wide-angle end to the telephoto end; and A rear fixed lens group (G4) with a negative optical power that is fixed during zooming, which is used for focusing and compensating for the thermal defocus of the optical system in high and low temperature working environments; A secondary imaging lens group (G5) with a positive optical power that is fixed during zooming, which is used to realize the front placement of the cold stop of the infrared cooled detector; Among them, when zooming from the wide-angle end to the telephoto end, the zoom lens group (G2) and the compensation lens group (G3) move towards each other, and the interval between the two components satisfies the following conditions: (d 23max -d 23min ) / f w >1 Wherein: f w is the focal length of the wide-angle optical system; d 23max is the maximum value of the interval between the zoom lens group (G2) and the compensating lens group (G3) during zooming; d 23min is the minimum distance between the variable magnification lens group (G2) and the compensating lens group (G3) during variable magnification; Among them, the lens groups (G1), (G2), (G3), (G4) and (G5) all adopt aspherical designs to balance the high-order aberrations of the optical system, and the optical power distribution is a positive-negative-positive-negative-positive structure; the zoom lens group (G2) is a diffractive surface lens with an aspherical substrate, which is used to correct the chromatic aberration and secondary spectrum of the optical system; the focal length is continuously variable from 110 mm to 1500 mm; Optical system design parameter table 2. The ultra-long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, characterized in that, The working wavelength range of this optical system is 3.7 - 4.8 μm, and the F# is 4.

3. The ultra-long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, wherein This optical system is adapted to a mid-wave infrared detector with an F-number of 4, a pixel number of 1024×768, and a pixel size of 10 μm or more.

4. The ultra-long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, characterized in that, The front fixed lens group (G1) with a positive optical power that is fixed during zooming includes a lens (L11) with a positive optical power and a lens (L12) with a negative optical power. At least one surface of the two lenses is meniscus-shaped and curved towards the detector target surface.

5. The very long focal length high resolution continuous zoom mid-wave infrared optical system according to claim 2, characterized in that, The other surface of the lens (L11) with a positive optical power is aspherical.

6. The very long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, wherein The lenses in the zoom lens group (G2) and the compensation lens group (G3) are all aspherical lenses, and at least one surface is an aspherical diffractive surface.

7. The ultra-long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, characterized in that, The rear fixed lens group (G4) with a negative optical power that is fixed during zooming includes a meniscus-shaped lens. The bending direction of the lens is towards the object side, and its first surface is aspherical.

8. The very long focal length high-resolution continuous zoom mid-wave infrared optical system according to claim 1, characterized in that The secondary imaging lens group (G5) with a positive optical power successively includes, from the object side to the image side, a double convex lens (L51) with a positive optical power, a meniscus-shaped lens (L52) with a negative optical power, and a meniscus-shaped lens (L53) with a positive optical power. At least one surface of at least one lens is aspherical.

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